my mum wouldn't have her ears tested, and it was becoming so hard she couldn't hear properly on the phone, or in person. It got to the point when she was actually sounding like she was coming down with dementia because she'd answer a question she thought you'd asked; she gets visits from the community matron and at one point they said to her we're going to syringe your ears, put drops in for so many days and we'll come and do it, she did and they did, immediate improvement with hearing, they did the same again, now she can hear really well, the third appointment has been on hold because of corona, but I'm so glad that she had it done, and actually so is she. It took a nurse telling her they were going to do it, she will do things for the doc or nurse say she needs to, is your Dad like that?
Having it done properly rather than just drops is the key, and it would need to be done before a test anyway. My Dad at one point went for a private hearing aid which to be honest was not really that good and half the time he had to take it in for adjustment, but eventually again the nurse got him sorted for a proper NHS test [after decking them] and the NHS one was so much better, and as discreet as the private one. Do go via the NHS, even if he has a test at boots or specsavers. Maybe you ould go with him.
What does he do? Is it something that the employer would prefer if he could hear better [or is a safety issue].
My Dad had a disabled railcard because of his deafness, and that entitled him to bring a helper who would also get a reduction, so he never bothered with a senior railcard as he could bring mum along and she didn't need one either, on a station it's a safety issue, and also a practical one, if you can't hear the announcements
He can always not use an aid if he is with someone with whom he doesn't want to look old but I suspect his quality of life will improve so much if he can hear again that it will not be a problem
I know some people who have aids and you can't see them, until they said I didn't know they had them